It isn't a tour-de-force of in-depth hardcore technical security topics. Instead the aim was to pull together some of the many concepts that are often encountered when creating a Silverlight (or indeed, any RIA) application.

Since the article was published I came across a similar (though thankfully not too overlapping) security paper from Nick Kramer who works on the silverlight team. Here's his blog post introducing the paper: Silverlight security overview paper has been officially published. It gives a lot more detail on client side security (and reasons decisions where made by the Silverlight team) whereas mine focusses primarily on the Services your application would consume.